(1) Field of the Invention
This invention generally relates to an exhaust gas cleaning device for diesel engines of motor vehicles, and more particularly relates to a device having filter means capable of physically catching carbon particles or the like (hereinafter, referred to as exhaust particles) contained in the exhaust gas and means for burning and removing periodically the caught exhaust particles, thereby regenerating the capability of the filter means.
(2) Description of the Prior Arts
Exhaust particles in the exhaust emmisions of diesel engines contain considerable amounts of combustible substances, such as carbon particles or the like, as well as other harmful substances. Hitherto, various kinds of devices have been proposed and used for catching such combustible particles by using an appropriate filter element and then burning and removing the caught particles in order to restore the capability of the filter elements. Especially, the methods described below are known in the prior art and there are some defects in each method.
1. A method for throttling an intake passage to reduce the flow of suction air and to raise the temperature of the exhaust gas, thereby burning the exhaust particles contained therein. According to this method, when the engine is running at a heavy load condition the temperature of the exhaust gas is raised enough so that it is possible to burn the exhaust particles. However, when the engine is running at a low load condition, the temperature of the exhaust gas is not raised enough and, therefore, it is impossible to burn out the exhaust particles and to regenerate the capability of filter material.
2. A method for providing an oil burner in the exhaust system and for raising the temperature of the exhaust gas to burn the exhaust particles. According to this method, a large amount of hydrocarbon (HC) is generated when the burner is ignited and, therefore, there are some problems relating to the durability, safety, cost and so on of the oil burner. There has also been known a system having dual exhaust systems, in which the flow of the exhaust gas is stopped in either of the exhaust systems and the exhaust particles are burned in the exhaust system in which the exhaust gas has been stopped. Such a system is, however, expensive and complicated in construction.
3. A method for providing electric heaters on the surface of the filter material to ignite the exhaust particles attached thereto and to introduce the energy thus released to the inside area of the filter to burn the exhaust particles accumulated therein. According to this method, a considerable amount of electricity is required, since the electric heaters must be attached to the entire surface of the filter material, so that it is not feasible to employ this device in motor vehicles. In order to reduce the consumption of electricity, the exhaust system must be a so-called dual type, in which one of the exhaust passages is closed to stop the flow of the exhaust gas, so that the exhaust particulates accumulated in a filter of the closed exhaust passage can be burned. Such a system is, however, complicated in construction and expensive.